This invention relates to systems which automatically control the power input to a motor making it commensurate with loading on the motor to thereby increase the efficiency of the motor.
In the aforementioned parent application there was described a power factor controller for an AC induction motor. The system described samples line voltage and current through the motor and decreases power input to the motor proportional to the detected phase displacement between the current and voltage to thereby provide less power to the motor as it is less loaded.
In one embodiment described there is an analog power factor circuit which includes a start up circuit which responds to the initial energization of the motor for maintaining the "ON" time of a triac in series with the motor at maximum in order to enable the motor to reach full speed in minimum time. The specific circuit described for achieving that purpose included a one-shot which responds to the initial energization of a power supply in order to provide a voltage which insures full turn on for an initial energization.
While such circuit is effective during initial turn on, it would be beneficial if the same circuit which provides full voltage to the motor during turn on would also be available for use when sudden loads are applied to the motor during normal operation. In such situations, the controller should also apply full voltage to the motor for a short time to prevent stalling.
In another embodiment in the aforementioned copending application, there is described a digital power factor circuit. Such circuit, however, is not completely digital in that the reference saw tooth waveform is provided by an analog ramp generator. Additionally, the circuit which provided the initial offset for full load lag provided a fixed offset. However, it is known that such full load phase lag varies for each motor and accordingly should be set on the controller in accordance with the specific motor being utilized. Additionally, the number of output pulses provided to the triac was an integral number of the cycles of input voltage. It would be beneficial if the number of pulses could be controlled so as to be sent either once or twice per cycle. This would provided improved response time and greater accuracy which would produce more efficiency.
Accordingly, although the aforementioned copending application provides numerous novel features, the present invention provides additional improvements over such power factor controller circuits which are described.